zombies can't climb, but can they crawl?

In most zombie films and the majority of zombie wargames I have seen (all three of them! :-P ) zombies can't climb, or only one in six can climb.

 This is very useful as it means you can barricade a place to the best you can do and use ladders to get into buildings and safe houses.

 It also means fire escapes on the side of buildings are useful - I hope to be making some for some of my buildings.

But - can  zombies crawl? We have seen the ones without legs crawling - they have no say in the matter. But what about the others? Can they get down and crawl?

If they can't crawl then many other 'zombie proof' ideas come to mind, especially for you safe house/base.

Tunnels - a net work of narrow tunnels rather like those the Viet Cong had during the Vietnam war (only maybe not so many of them, or full of nasty traps) could be a great way to go in an out of safe houses you do have to say to mum "it followed me home, can you shoot it?"

Small holes in barricades could make it easier to get in and out without the need to open up big wide doors in the barricade, thus keeping some of the barricade's integrity. 

Mind you, tunnels don't help when it comes to bringing in bulky items you have scavenged, and you can't drive a vehicle through them, but they could be good as an emergency escape plan.